Low NOx combustors for gas turbines are known in the industry. For example, U.S. Pat. No. 4,292,801 describes a “Dual Stage-Dual Mode Low NOx combustor” that creates reduced amounts of nitrogen oxide (NOx) during the combustion process. Such a low NOx combustor generally includes two combustion chambers. Fuel is introduced into the chambers through fuel nozzles that extend through an end cap of the combustor. More specifically, a number of primary fuel nozzles extend into a first combustion chamber and a secondary fuel nozzle extends toward a second combustion chamber. In operation, fuel is selectively introduced through the primary and secondary fuel nozzles to initiate and terminate combustion in the corresponding chambers. The combustion may be controlled in a manner that generates a relatively low level of NOx.
Each primary fuel nozzle typically includes a nozzle body, an orifice plate, and a collar. The orifice plate is positioned on an interior of the nozzle body and fuel flowing through the nozzle body passes through orifices in the orifice plate. The collar is positioned on an exterior of the nozzle body adjacent an exit end. Fuel flowing through the nozzle body passes through the exit end adjacent to the collar. The orifice plate and the collar affect the flow characteristics of the fuel and therefore the performance of the combustor.
Typically, the orifice plate and the collar are coupled to the nozzle body using a process such as brazing or electron beam welding. These processes make the orifice plate relatively difficult to remove. However, the flow of gas and air through the orifice plate may abrade the orifices so as to impact the performance of the combustor. In such a case, the primary fuel nozzle may be replaced. Further, these processes may create a fillet at the points where the collar and the nozzle body are joined. The fillet may have an uncontrolled size, shape, and surface, which may disturb the flow of fuel and air flow adjacent to the exit end of the nozzle body, again affecting the performance of the combustor.